So the history goes like this. We have a watershed exhibit that used to have rainbow trout in them, but you need to get a permit from DFW and have to take a class to get it. We have a staff member who did this but could never get in touch with the guy at DFW to get the trout and the tank stayed empty.
I started putting tilapia (mozambique species) in there because they are found in a lot of local lakes as well as storm drains. They are also able to handle different salinities, I collected some from a lagoon and then had them in pure sea water and pure freshwater and both survived.
Tilapia are hardy, they are one of the most widely used fish in farm raising. I got twenty fry from a guy nearby thinking only half or less might survive. Every single one survived and grew to adults and I had to give most away to one of my buddies who had a pond. I grew probably 4 generations of fish and had the smaller ones on display and then had a crash a few summers ago when it got really hot in so Cal. Most of my males didn't make it and the remaining two beat the shit out of each other and then I was out of males.
Another guy was raising some locally and I went to pick up a male. He had a aquaponics set up where veggies were growing in the filter bed, and the fish were in the sump below and this was in a six foot bed in his backyard. I've been wanting to do this for years, I saw a display at Epcot maybe 20 years ago and was impressed then but never pursued it. I talked to my chief Aquarist and my director and they said give it a go so I started researching the methods.
There are a lot of substrates you can use, but I chose crushed lava rock over hydroton because it is very cheap and available. I got the tilapia from yet another breeder who has a gigantic greenhouse and raises veggies and fish for his restaurant. The hardest part was designing a draining system, most guys use what is called a "bell sipon" but there are a few problems with the design so I started trying different siphon designs. The problem with any type of siphon is the water coming in has to be slower than the water going out, otherwise you end up in equilibrium where the water just sits midway in your grow bed. I tried out a series of designs and ended up basing mine on a Carlson siphon with a few changes, I call it the Oakpwr Siphon
.My siphon is set up in your typical u fashion with a 3/4" main drain. When I ran this I always had problems with the system draining fully, no matter the flow rate it almost always went to equilibrium where the water in was the same rate as the water out and it never fully drained. I ended up adding a second smaller 1/2" drain connected to a T. Basically what I am saying is I have two drains, the main drain which siphons most of the water and the second smaller drain connected to it makes enough pull to break the siphon when the water gets to the bottom of the grow bed. At this time the water stops draining into the sump where the fish are and the process starts again.
I will point out that it is possible to grow certain plants without a bed, but from what I read you get maximum growth using a ebb and flow bed to expose the roots to oxygen. I wanted that so that's what I went with.
The results are pretty cool, I went with carrots and lettuce on the first run. The carrots were a mistake, I need a deeper bed to get proper root growth but they flourised. The lettuce was doing GREAT until the raccoons climbed the fence and ate most of my lettuce. Lesson learned, I put a roof over the enclosure and will try it again.
The neat things about this design:
1. soilless. It requires no soil and no nutrients besides fish waste
2. fairly idiotproof. Since it is based on a siphon rather than any moving parts, the drain is less likely to fail
3. can be converted to solar. I'm getting ready to change out that pump I'm using to a slower flow rate (I used one of our extra magnetic drive pumps and valved the flow waaaay down). It looks like I can do a dc pump for about 20$ on amazon, but I will need 45W solar panel which is a bit expensive, plus a back up battery for nighttime use.
4. You can easily do this at home and grow your own veggies and fish. Many types of freshwater fish and shrimp can be grown this way. There are large scale versions of this set up pumping out 100 heads of lettuce a day.
5. I use a protein pellet type of food but you can use duckweed for tilapia and they will eat this readily and you can also feed them alternative types of food ie it's cheap to run.
6. The main point is this. It wakes people up and you can discuss the problems with overfishing, farming using too much water and wasting it as it runs over the soil etc. You would never be able to eat a large amount of tilapia from a small system, but you could eat them once in a while. There are different species with different growth rates and that's going to be in my next trial as well.
